1. Field of the Invention
The present invention relates to a method for manufacturing toner for developing electrostatic latent images. Specifically, the present invention relates to a method for manufacturing toner for developing electrostatic latent images having excellent image characteristics even with repeated copying when used to develop electrostatic latent images in electrostatic printing, electrostatic recording, and electrophotography.
2. Description of the Related Art
Emulsion dispersion is one type of method for manufacturing resin microparticles. This method produces resin microparticles by subjecting a resin solution produced by dissolving resin in a non-water soluble organic solvent to emulsion dispersion in an aqueous dispersion fluid under atmospheric pressure to form an oil-in-water (O/W) type emulsion, and heating this emulsion under continuous agitation to vaporize and remove the organic solvent. This emulsion dispersion method is capable of producing resin microparticles having an average particle size of approximately 1 to 10 .mu.m via a relatively simple operation in a simplified process, thereby reducing costs while improving production efficiency compared to pulverization methods and suspension polymerization methods. Furthermore, more types of resins are usable compared to the suspension polymerization methods.
Consequently, this emulsion dispersion method has been proposed to disperse toner components such as colorant, charge controller, magnetic powder and the like in a resin fluid as an inexpensive and relatively simple method to produce toner for developing electrostatic images in accordance with user needs for color, high image quality, high speed developing and the like in printers and photocopiers of the electrophotographic type. For example, Japanese Laid-Open Patent Application Nos. SHO 61-91666 and SHO 63-25664 disclose methods for manufacturing toner for developing electrostatic images via the aforesaid emulsion dispersion method.
Toners for developing electrostatic images produced by the aforesaid emulsion dispersion method are disadvantageous in that image quality is affected due to some filming and fogging of the copy images from the start, and more marked fogging and filming after repeated copying.
On the one hand, this method produces resin microparticles by subjecting a resin solution produced by dissolving resin in a non-water soluble organic solvent, forming an oil-in-water (O/W) type emulsion produced by adding an aqueous dispersion fluid to the resin solution under atmospheric pressure, heating this emulsion under continuous agitation to vaporize and removing the organic solvent, disadvantages in that image quality (image stability) is affected, particularly when making repeated copies, similar to the aforesaid emulsion dispersion of resin solution in an aqueous dispersion fluid.